The rapid acceptance of computer technology by corporations as well as consumers has led to the widespread use of computers. Further abetting this process is the continual reduction in size and cost of personal computers. Originally, personal computers were large items best suited for floor standing or desktop use. Eventually, they became smaller so that desktop use became the standard. Improvements in processor, memory and data storage capabilities have resulted in light weight, powerful mobile computers such as portables, laptops, notebooks, palm top and personal digital assistants. These computers can provide sufficient processing capability for audio visual applications, such as computer aided design, three dimensional animation, and multimedia presentation, even when used at remote locations.
Typically, many users of such mobile computers also own desktop computers used for applications that manage databases similar to the databases carried in mobile computers. Normally, the user adds data to the two computers independently, e.g., one enters data into the mobile computer, often referred to as a client, when out at a customer site but enters data into the desktop computer or a network server when in the office. In such cases, the user normally would at some point want to keep these two sets of data identical, especially if different changes are made in parallel to both devices. This action is called data synchronization.
FIG. 1 illustrates a block diagram of a client/server system for data synchronization. As is shown, the client 10 includes a database 12, which ideally is in sync with a server database 22 at the server 20. Typically, the client 10 requires a client database adapter 14, which is a large piece of software, installed to retrieve and add data during a synchronization. The data is exchanged in a format that the client 10 and server 20 are both able to generate and to parse. The client 10 needs to create and to parse the document 19 which requires a certain amount of code on the client 10 device. Especially with today's mobile clients 10, like mobile phones or small handheld computers, the resources available are very limited. Adding flash memory to the mobile clients is an option, but a very costly one.
A client 10 that wants to synchronize its data with the data of a server 20 also needs a local client sync engine 16 that retrieves the adds, changes, updates, etc. from the client's database 12 and creates a standardized document 19 to tell the server 20 which data has been added, deleted, etc., on the client's side 10. The server 20 parses this document 19 and updates the server (or host) database 22 accordingly. The server 20 also checks the host database 22 for changes which might have taken place since the last synchronization cycle with the respective client 10, retrieves these records and builds the exchange document 19. The client 10 will receive this document 19 and now needs to parse it to know what to do.
Thus today, a client 10 needs at least the following three components shown in FIG. 1 to synchronize data with a server 20: a client database adapter 14, a sync client agent 16 and a client sync adapter 18. The sync adapter 18 contains an encoder and a parser (not shown) to generate and understand the standardized exchange document 19.
One Industry Data Synchronization Standard is SyncML. SyncML includes a universal data synchronization format that is defined by an Extensible Markup Language (XML) document type, XML being a standard format for interchanging structured documents. This format is exchanged as SyncML messages between network devices. A SyncML message is just an XML document. SyncML is independent from the underlying transport layer and can be used in wireless as well as in wired environments.
Unlike HTML, XML enables the creation of user defined tags. Traditional HTML tags are extended by user defined elements. Like in HTML, the start and end of each logical block is marked by the appropriate tags. Document Type Definitions (DTD) are an important element of XML. They define the role of text elements in a formal model. The DTD can be used to check if an XML document contains valid tags and if the tags occur in the right place within the document. It also specifies the attributes that belong to an element and the valid values of these attributes. Thus, DTDs have two main functions:                1) specifying which document structures can be used by the author of an XML document and which document structures have to be handled by the generator that creates that defined kind of XML document; and        2) specifying which document structures have to be handled by parsers that process that defined kind of XML document.        
In Standard Generalized Markup Language (SGML), of which XML is a subset, the use of DTDs is required. However, XML does not require the use of a DTD. A parser that processes a document without a DTD has to extract the relevant information from the document itself.
The statement that XML is “extensible” can be misunderstood. XML defines a syntax, in the form of a number of rules in order to define document structures. These rules are defined in the XML specification and cannot be extended. “Extensible” means that special instances of tag languages can be built on the fundamental rules of XML.
The basic concept of XML is the composition of documents using a series of entities. The entities themselves are composed of one or more logical elements. The elements can contain attributes which describe the way in which the elements have to be processed.
In addition, SyncML defines a synchronization protocol. This protocol specifies how SyncML conformant messages are exchanged to synchronize databases on different network devices. The synchronization protocol supports both one-way, as well as two-way data synchronization. The SyncML specifications also define HTTP, OBEX, and WSP transport bindings, which describe the minimum set of features that a SyncML compliant transport implementation must support.
In U.S. Pat. No. 5,974,238, an apparatus for performing dynamic synchronization between data stored in a handheld computer and a host computer is disclosed. Each computer includes a plurality of data sets including at least one common data set, and each computer includes a copy of the common data set. The handheld computer comprises a data synchronization engine having a pseudo-cache and one or more tags connected to the pseudo cache. Data is synchronized whenever data is written to main memory and/or when the associated pseudo-cache tag is invalidated. By strict adherence to a set of protocols, data coherency is achieved because the system always knows who owns the data, who has a copy of the data, and who has modified the data. A data synchronization engine resolves any differences in the copies and allows the storage of identical copies of the common data set in the host computer and in the handheld computer.
In U.S. Pat. No. 5,684,990, a data processing method for synchronizing the data records of a plurality of disparate databases is disclosed, in which a status file is provided containing data records representative of the contents of data records existing in the disparate databases at a prior synchronization. Data records from at least a first and a second of the plurality of databases are compared to corresponding data records of the status file to determine whether data records of the plurality of databases have changed or been deleted since the prior synchronization, or whether there are new data records since the earlier synchronization. Based on the outcome of the comparing step, decisions are made as to how to update the data records of the first and second databases. Finally, the status file is updated so that its data records are representative of the contents of the data records of the first and second databases after they have been updated.
These synchronization systems possess at least one disadvantage in that they do not take into account that mobile clients like mobile phones, have very restricted storage capacity. The components necessary for the systems according to the state of the art require a lot of storage capacity on the side of the client device. In addition, a fixed protocol and document format is used that the client needs to convert the data to and from.
Thus, there exists a need for a method and system for synchronizing data between a server and a client that reduces the amount of code needed on a client to synchronize data with the server system. There is also a need for a method and system for synchronizing data that allows the client to send data to the server system in a format most suitable for the client device, and frees the client device from having to parse the exchange document. The present invention addresses these needs.